Survey of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products by commercial real-time PCR kits

Real-time PCR (RTiPCR) assays including enrichment stage were evaluated for the rapid detection of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products using molecular beacon probes available as commercial kits (WARNEX Genevision, Canada & AES Chemunex detection system, France). The accuracy of the assays was evaluated analyzing 1032 naturally contaminated food samples in combination to the conventional cultural methods. Presence/absence testing of the above pathogens was performed in 25 g samples of each product. In case of L. monocytogenes of 39 positive RTiPCR samples, 37 were confirmed by the cultural method (based on McNemar's test the difference between the two methods is insignificant). The highest incidence of L. monocytogenes in food products was found in desserts and the second highest in frozen pastries. None of the samples were cultural positive but negative in the RTiPCR test. One among the 343 investigated samples was positive for Salmonella spp. by RTiPCR and the cultural method. Out of 333 samples analyzed for E. coli O157:H7 no positive sample was detected. RTiPCR-based methods proved to be powerful tools for fast, sensitive and accurate pathogen detection in raw food ingredients and ready-to-eat products.     

Prevalence of Listeria spp. in Traditional Indian Dairy Products from Chennai Metropolis,Tamil Nadu

The present study was conducted between September, 2014 and June, 2015 to assess the prevalence of Listeria monocytogenes in Traditional Indian Dairy Products from Chennai, Tamil Nadu. Samples of Ghee, Rasagolla, Gulabjamun, Curd and Payasam were screened for the presence of L. monocytogenes using conventional culture method and validated by PCR. Among the 150 samples screened, 50 isolates from different dairy products (22 gulabjamun, 22 rasagolla and 06 curd samples) were presumptively identified as Listeria spp. Further confirmation by biochemical characterization and hemolysis on blood agar revealed that 34 isolates were Listeria welshimeri, 10 were L. murrayi and 06 were identified as L. seeligiri. The 34 isolates of L. welshimeri were present in 14 gulabjamun, 14 rasagolla and 06 curd samples. Similarly, 10 isolates of L. murrayi have been found in 04 gulabjamun and 06 rasagolla samples. L. seeligiri isolates were identified from 04 gulabjamun and 02 rasagolla samples. None of the Listeria species were found in ghee and payasam samples and interestingly, the results of both methods revealed that none of the traditional products screened were positive for L. monocytogenes     

Incidence of Listeria in Egyptian meat and dairy samples

A total of 180 food samples including meat (raw lean beef, frozen lean beef, and frozen chicken) and dairy products (raw milk, Zabady and Kareesh cheese) were analysed for Listeria. Isolates were differentiated using morphological, cultural, and biochemical tests and an API-Listeria kit. Zabady cheese was completely free of Listeria. The highest incidence rate (13.33%) was in frozen lean beef. Raw lean beef and milk products showed an incidence rate of 6.67%. The lowest incidence rate (3.33%) was in Kareesh cheese and frozen chicken meat samples. L. monocytogenes showed the lowest incidence rate (0.55%), isolated from one frozen lean beef sample. L. ivanovii and L. grayi showed the highest incidence rate (2.22%), isolated from 4 samples. L. innocua and L. seeligeri were positive in 3 samples (1.67%), and L. welshimeri in 2 samples (1.11%). L. monocytogenes and L. ivanovii were positive for virulence factors (hemolytic properties, and extracellular enzyme activities).     

Longitudinal monitoring of Listeria monocytogenes contamination patterns in a farmstead dairy processing facility

Contamination of dairy products with Listeria monocytogenes is a concern because multiple human listeriosis outbreaks have been linked to contaminated cheese and dairy products. Dairy production on farmstead operations may be a particular concern because L. monocytogenes is also an animal pathogen that can be shed by ruminants with and without clinical symptoms; physical proximity between production animal and dairy processing facilities may thus provide a higher risk for introduction of L. monocytogenes into the dairy production process. To better understand the risks of L. monocytogenes contamination associated with farmstead dairy production, samples from a farmstead dairy processing operation and the milking barn of the directly adjacent dairy sheep operation were tested for L. monocytogenes over a 3-yr period. Prevalence of L. monocytogenes for samples collected on the farm (n = 85) and the dairy production facility (n = 674) was 9.4 and 2.7%, respectively. Molecular subtyping using automated EcoRI ribotyping of L. monocytogenes isolates revealed that distinct subtypes were associated with the dairy production facility and the farm's milking parlor. Although a total of 5 and 4 different ribotypes were identified among isolates obtained from the dairy production facility and the milking parlor, respectively, only 1 ribotype (DUP-1030A) was isolated from both. Different ribotypes were predominant among isolates from the dairy production facility (ribotype DUP-1052A, representing 15 of 18 isolates) and the farm's milking parlor (ribotype DUP-1039A, representing 4 of 8 isolates); each of these ribotypes appeared to persist over time in the respective area. Our data support that i) in farmstead dairy processing facilities, L. monocytogenes present on the farm can largely be prevented from being introduced into the processing facility; and ii) L. monocytogenes can persist on farm and in processing areas, providing a potential high-risk source for contamination. Preventing cross contamination between dairy production and processing facilities and control of persistent L. monocytogenes are thus critical to assuring the microbial safety of farmstead dairy products.     

Listeria monocytogenes and ready-to-eat seafood in Spain: Study of prevalence and temperatures at retail

The aim of this study was to obtain data from refrigerated ready-to-eat seafood products at retail in Spain (young eels, crabstick and smoked salmon), regarding prevalence and levels of Listeria monocytogenes, storage temperatures and the impact of transport conditions (type of bag) on the temperature of the product. The one-year surveillance period was carried out according to the EC Regulation No. 2073/2005, taking 5 units/batch and analyzing 250 samples following ISO 11290-1/A1 and ISO 11290-2/A methodologies. Low prevalence of L. monocytogenes was observed in surimi products, while 4.8% of smoked salmon samples were positive for Listeria with low levels (<10 cfu/g) and uneven pathogen distribution. A single company was responsible for 80% of the positive lots. All purchased products showed values higher than 4 °C at retail and an average increase of 2.5 °C or up to 6.2 °C was recorded when isothermal or plastic shopping bags were used for transport, respectively. To avoid noncompliance of the Food Safety Objective for L. monocytogenes in seafood RTE products more efforts from all stakeholders are needed, with special attention so as to improve control and maintenance of refrigerators at retail and to enhance consumer education regarding food safety practices.     

Combination of growth conditions and InlB-specific dot-immunoassay for rapid detection of Listeria monocytogenes in raw milk

The gram-positive bacterium Listeria monocytogenes is an important foodborne pathogen contaminating dairy products. Closely related to L. monocytogenes saprophytic Listeria spp. are also frequent contaminators of food and, particularly, dairy products. To distinguish L. monocytogenes from nonpathogenic Listeria spp. and other bacteria, a dot-immunoassay was developed. The immunoassay is based on the polyclonal antibody to the secreted form of the surface virulence-associated L. monocytogenes-specific InlB protein. To increase InlB production, bacteria were grown on the brain-heart infusion agar supplemented with 0.2% activated charcoal (BHIC agar). Direct plating of artificially contaminated raw milk samples on the BHIC agar followed by the dot-immunoassay allowed a rapid identification of L. monocytogenes in concentrations as little as 10 cfu/mL. Using the developed approach, preliminary results were obtained within 14 h, and the final results were obtained after 26 h. The dot-immunoassay was tested on L. monocytogenes strains belonging to different clonal complexes and phylogenetic lineages, Listeria spp., and other bacterial species. Results showed the exceptional specificity of the developed dot-immunoassay for the rapid identification of L. monocytogenes.     

Detection and characterization of Listeria monocytogenes in Sao Jorge (Portugal) cheese production

Listeria monocytogenes is a foodborne pathogen that can cause serious invasive disease in humans. Because human listeriosis cases have previously been linked to consumption of contaminated cheese, control of this pathogen throughout the cheese production chain is of particular concern. To understand the potential for L. monocytogenes transmission via São Jorge cheese, a Portuguese artisanal cheese variety that bears a Protected Denomination of Origin classification, 357 raw milk, curd, natural whey starter, and cheese samples representative of the production chain of this cheese were collected over one year and tested for the presence of L. monocytogenes and selected physicochemical parameters. Although neither L. monocytogenes nor other Listeria spp. were detected in whey, curd, or cheese samples, 2 of the 105 raw milk samples analyzed were positive for L. monocytogenes. These 2 raw milk isolates represented a ribotype that has previously been linked to multiple human listeriosis outbreaks and cases elsewhere, indicating the potential of these isolates to cause human listeriosis. On average, physicochemical parameters of São Jorge cheese ripened for 4 mo presented values that likely minimize the risk of L. monocytogenes outgrowth during ripening and storage (mean pH = 5.48; mean moisture = 37.79%; mean NaCl concentration = 4.73%). However, some cheese samples evaluated in this study were characterized by physicochemical parameters that may allow growth and survival of L. monocytogenes. Even though our results indicate that raw milk used for São Jorge cheese manufacture as well as finished products is rarely contaminated with L. monocytogenes, continued efforts to control the presence of this pathogen in the São Jorge cheese production chain are urged and are critical to ensure the safety of this product.     

Prevalence and characterization of antimicrobial resistance of foodborne Listeria monocytogenes isolates in Hebei province of Northern China, 2005-2007

A total of 2177 food samples collected from nine cities in northern China during 2005 to 2007 were screened for the presence of Listeria monocytogenes. All L. monocytogenes isolates were subjected to serotyping, antimicrobial susceptibility, pulsed-field gel electrophoresis (PFGE), as well as PCR screening to identify genes responsible for tetracycline resistance [tet(L), tet(M), tet(K), tet(S) and tet(B)], transposon Tn916, and class 1 integron. Contamination with L. monocytogenes was detected in 4.13% (90/2177) of the total samples representing various food products. The pathogen was mainly isolated from frozen food made of wheat flour or rice products (26/252, 10.32%) and raw meat products (46/733, 6.28%). Besides, 3.31% (10/302) of cooked meat, 1.17% (4/343) of seafood, 0.98% (2/204) of non-fermented bean products and 0.62% (2/323) of vegetables samples were contaminated by this bacterium. The L. monocytogenes isolates belonged to five serotypes (1/2a, 1/2b, 1/2c, 4b, and 3a), with serotype 1/2a being dominant (48.88%). Antimicrobial resistance was most frequently observed for ciprofloxacin (17.8%), tetracycline (15.6%) and streptomycin (12.2%). Overall, resistance was observed against 14 out of 18 antimicrobials tested while multiple resistances occurred among 18.9% (17/90) isolates. Interestingly, two isolates were resistant to more than five antimicrobials. Among 14 tetracycline-resistant isolates, 13 carried tet(M) gene including nine possessing Tn916, and one harbored tet(S) gene. PFGE analysis revealed genetic heterogeneity among individual serotypes as well as scattered occurrence of some genotypes without any clear-cut correlation to source or food type. The widespread distribution of epidemiologically important serotypes (1/2a, 1/2b and 4b) of L. monocytogenes, and their resistance to commonly used antibiotics indicate a potential public health risk. Our data also indicate that L. monocytogenes could act as a reservoir of mobile tet genes along the food chain.     

A multiplex PCR assay based on 16S rRNA and hly for rapid detection of L. monocytogenes in Milk

A multiplex PCR assay was developed by targeting ‘16S rRNA’ and ‘hly’ genes for detection of Listeria or Listeria monocytogenes in dairy foods on the basis of amplification of 1200 and 713 bp products, respectively. The assay conditions were optimized to make it truly rapid and to cut down the cost. The authenticity of the multiplex PCR was ascertained by using Nested PCR targeted against internal region of ‘hly’ gene that produced an amplified product of 188 bp. The multiplex PCR assay was found to be specific for detection of L. monocytogenes only since none of the non-listerial cultures gave positive signal. The sensitivity of the multiplex PCR was limited to 10 ng pure DNA and 1–10 cells of L. monocytogenes after 4–6 h enrichment in Listeria enrichment broth. When applied to 20 raw milk and 10 pasteurized milk samples, L. monocytogenes could not be detected in any of the samples by the multiplex PCR assay. This assay could find potential application in dairy industry for monitoring dairy foods for this high risk food pathogen on routine basis.     

Occurrence of Listeria Monocytogenes in a Serbian Salmon and Seafood Processing Line During 2013

The objective of this study was to examine the occurrence of L. monocytogenes in a selected fish and seafood processing line. Results showed that during 2013, 12.4%, 8.3% and 2.3% of fish, seafood salads and environmental swabs were positive for L. monocytogenes. All positive food samples showed a contamination level below 100 CFU/g. Environmental swabs from surface of slicing and trimming tables, slicing machines, fish filleting and trimming knives, belt glazer and working table were positive for L. monocytogenes. Therefore, strict attention must be paid to cleaning and disinfection to control the level of L. monocytogenes.     

High prevalence,low counts and uncommon serotypes of Listeria monocytogenes in linguiça, a Brazilian fresh pork sausage

Linguiça is a highly popular and appreciated pork product in Brazil, frequently consumed undercooked. Aiming at collection of data for a future risk assessment, this study evaluated the prevalence and counts of Listeria monocytogenes in linguiça samples collected at retail level in Sao Paulo, SP, Brazil. ISO methods were used for detection and enumeration of the pathogen (11290-1 and 11290-2, respectively). Isolates were submitted to Simplex-PCR for hlyA gene and those with biochemical features of L. monocytogenes and hlyA positive were serotyped using a Multiplex PCR. Ninety percent of the samples were positive for Listeria spp., and L. monocytogenes was detected in 42% of the samples, with counts below 10² CFU/g in all samples. A prevalence of uncommon serotypes 4a and 4c was observed.     

Quantification of Listeria monocytogenes in minimally processed leafy vegetables using a combined method based on enrichment and 16S rRNA real-time PCR

Modern lifestyle markedly changed eating habits worldwide, with an increasing demand for ready-to-eat foods, such as minimally processed fruits and leafy greens. Packaging and storage conditions of those products may favor the growth of psychrotrophic bacteria, including the pathogen Listeria monocytogenes. In this work, minimally processed leafy vegetables samples (n = 162) from retail market from Ribeirão Preto, São Paulo, Brazil, were tested for the presence or absence of Listeria spp. by the immunoassay Listeria Rapid Test, Oxoid. Two L. monocytogenes positive and six artificially contaminated samples of minimally processed leafy vegetables were evaluated by the Most Probable Number (MPN) with detection by classical culture method and also culture method combined with real-time PCR (RTi-PCR) for 16S rRNA genes of L. monocytogenes. Positive MPN enrichment tubes were analyzed by RTi-PCR with primers specific for L. monocytogenes using the commercial preparation ABSOLUTE™ QPCR SYBR^® Green Mix (ABgene, UK). Real-time PCR assay presented good exclusivity and inclusivity results and no statistical significant difference was found in comparison with the conventional culture method (p < 0.05). Moreover, RTi-PCR was fast and easy to perform, with MPN results obtained in ca. 48 h for RTi-PCR in comparison to 7 days for conventional method.     

Detection of Listeria spp. in faeces from animals,in feeds,and in raw foods of animal origin

Thirty-nine samples of feeds and 79 faecal samples were collected at seven different dairy farms, at some of which the cows were suffering from Listeria mastitis. Faecal samples were also collected from poultry on a dairy farm and from cages used for transportation of poultry to slaughter. Also neck-skin samples were taken from 17 carcasses of dressed poultry, and five samples of scalding and chilling water at a poultry slaughterhouse. Finally, 67 samples of minced beef were collected from retail shops. The overall results show that approximately 82% of the feed samples harboured Listeria spp. and 62% Listeria monocytogenes. The faecal samples showed that 67% harboured Listeria spp. and 51% L. monocytogenes. In the minced beef samples, Listeria spp. could be demonstrated in 67% and L. monocytogenes in 28%. Of the faecal samples from poultry, 33% harboured Listeria spp. and also 33% L. monocytogenes. Listeria spp. were detected in 94% of the poultry neck-skin samples, and L. monocytogenes in 47%. Almost all L. monocytogenes from faeces and feeds agglutinated Listeria antisera against serotypes 1–4, while only 71% of the strains from minced beef agglutinated the same antisera. The high prevalence of positive findings indicates that the isolation method used is suitable for detection Listeria spp. in heavily contaminated material as well as in foods with low bacterial counts.     

Evaluation of hygiene practices and microbiological quality of cooked meat products during slicing and handling at retail

Cooked meat ready-to-eat products are recognized to be contaminated during slicing which, in the last years, has been associated with several outbreaks. This work aimed to find out possible relation between the hygiene practice taking place at retail point during slicing of cooked meat products in small and medium-sized establishments (SMEs) and large-sized establishments (LEs) and the microbiological quality of sliced cooked meat products. For that, a checklist was drawn up and filled in based on scoring handling practice during slicing in different establishments in Cordoba (Southern Spain). In addition, sliced cooked meats were analyzed for different microbiological indicators and investigated for the presence of Listeria spp. and Listeria monocytogenes. Results indicated that SMEs showed a more deficient handling practices compared to LEs. In spite of these differences, microbiological counts indicated similar microbiological quality in cooked meat samples for both types of establishments. On the other hand, Listeria monocytogenes and Listeria inocua were isolated from 7.35% (5/68) and 8.82% (6/68) of analyzed samples, respectively. Positive samples for Listeria spp. were found in establishments which showed acceptable hygiene levels, though contamination could be associated to the lack of exclusiveness of slicers at retail points. Moreover, Listeria spp presence could not be statistically linked to any microbiological parameters; however, it was observed that seasonality influenced significantly (P < 0.05) L. monocytogenes presence, being all samples found during warm season (5/5). As a conclusion, results suggested that more effort should be made to adequately educate handlers in food hygiene practices, focused specially on SMEs.     

Prevalence and characterization of Listeria monocytogenes isolated from soft cheese

A survey was made in 1995–1996 for Listeria spp. in 63 soft cheeses, made from raw ewe's milk using traditional methods, in the Province of Beira Baixa (Portugal). Listeria spp. were isolated from 47 (75%) of the cheeses, L.monocytogenes was isolated from 29 (46%), and L.innocua but not L.monocytogenes from 18 (29%). Of 24 isolates of L.monocytogenes that were serotyped, 20 were serotype 4b, three were serotype 1/2b and one was serotype 1/2a. Phage typing of isolates of L.monocytogenes and L.innocua showed that in some cases a particular phage type was associated with cheese from a particular source. Twenty four strains of L.monocytogenes tested were able to grow at 30°C in culture medium adjusted with HCl to a pH in the range from 4.4 to 6.0 within 3 days; in the pH range 4.4–6.8 a representative strain grew most rapidly at pH 6.8. The pH range in the cheeses during maturation was between about 5.2–6.4. Whether L.monocytogenes could multiply in the cheeses would depend on factors such as concentration of organic acids and of salt, and storage temperature.     

Simultaneous Detection of Salmonella,Listeria monocytogenes,and Staphylococcus aureus by Multiplex Real-Time PCR Assays Using High-Resolution Melting

A method combining multiplex real-time polymerase chain reaction (PCR) with high-resolution melting (HRM) analysis for rapid and specific simultaneous detection of Salmonella, Listeria monocytogenes, and Staphylococcus aureus was developed. The method included a melting-curve analysis of products and was evaluated by specificity, sensitivity and reproducibility analyses. Sensitivity and reproducibility analyses was both conducted by genomic DNA extracted from serial dilutions for each target pathogen. Assays with artificially inoculated and naturally contaminated samples after enrichment were also conducted. In the specificity test, there was no nonspecific amplification of the 44 nontarget pathogens, whereas the actual T _m values were 79.38?±?0.14, 82.54?±?0.15, and 77.36?±?0.14 °C for Salmonella, L. monocytogenes, and S. aureus, respectively. The sensitivity of the method was 3.5?×?10² CFU ml^?1 for Salmonella and L. monocytogenes and 3.5?×?10³ CFU ml^?1 for S. aureus. The coefficients of variation of T _m values ranged 0.51–1.03 % for Salmonella, 1.63–2.11 % for L. monocytogenes, and 0.75–2.17 % for S. aureus in intraassay, and ranged 0.81–2.43 % for Salmonella, 1.97–2.35 % for L. monocytogenes, and 0.93–3.93 % for S. aureus in interassay. The detection limit in artificially inoculated samples (n?=?50) was 5 CFU (25 g)^?1 food for the three tested pathogens. In the naturally contaminated samples (n?=?120),Salmonella DNA was detected by HRM, sequencing, and conventional culture-based methods at a positive rate of 25.00, 25.00, and 24.17 %, respectively; the corresponding rates for L. monocytogenes were 14.17, 14.17, and 14.17 %, respectively, while those for S. aureus were 16.7, 16.7, and 16.7 %, respectively.     

The Antimicrobial Effect of Rosemary and Thyme Essential Oils Against Listeria Monocytogenes in Sous Vide Cook-chill Beef During Storage

Sous vide cook-chill (SVCC) is a technology characterized by vacuum-packaging of raw or partially prepared foods before pasteurization, followed by rapid chilling and storage below 3°C. The application of essential oils (EOs) is a strategy to control pathogens and to extend the shelf life of products by reducing microbial levels and oxidative processes. The aim of this study was to evaluate the efficacy of Rosmarinus officinalis L. (rosemary) Thymus vulgaris L. (thyme) EOs against L. monocytogenes ATCC 679, inoculated in beef processed by SVCC stored at 2°C and 8°C for 1, 2, 3, 7 and 14 days. Leaves were dried and hydrodistilled in a Clevenger. Determination of minimum inhibitory concentration (MIC) assay was performed. Beef samples of m. longissimus thoracis et lumborum were packaged in bags inoculated and added individually with one of each EO at MIC values. Bags were vacuum-sealed, and samples were processed at 55°C/65min (for 3-log₁₀ reduction). L. monocytogenes enumeration was done according to ISO 11290-2. A reduction of the population of L. monocytogenes was observed in all samples at 2°C. At day 14, the population of L. monocytogenes was similar in thyme and control at 2°C and 8°C. Inversely, rosemary at both temperatures show an added reduction of about 2-log₁₀, comparatively to control. These results support the possibility of using rosemary as natural preservative to contribute in the reduction of L. monocytogenes and confirm the importance of using adequate chilling storage for maintain this pathogen at acceptable levels in view to prevent the risk for consumers.     

Occurrence of Listeria species in raw milk in farms on the outskirts of Mexico city

Listerosis may be transmitted by direct contact with infected animals or by consumption of contaminated vegetables or meat and milk products. In Mexico, raw milk is widely consumed and the incidence of milkborne disease is unknown. A total of 1300 raw milk samples were obtained from 20 l bulk tanks at four different dairy farms in southeast of Mexico City from June 1998 to June 1999. The samples were enriched for 48 h at 30°C and plated onto McBride's Modified Agar (MMA). Suspect colonies were biochemically tested to confirm identity. Overall, 23% of all raw milk samples examined tested positive forListeria species; 13% were positive for L. monocytogenes (45·6% were serotype-4b and 54·4% were serotype 1); 6% for L. ivanovii; 4% for L. seeligeri and 1% forL. innocua. L. monocytogenes contamination was more frequent during the spring and summer months as isolation rates were 12·2% from June to October 1998 and 17% from March to June 1999. Serotype-4b isolates were not pathogenic for the mouse, while for serotype-1, strains DL₅₀ranged from 1·8×10⁶to 4×10⁷CFU ml⁻¹. Additional studies are needed to assess the public health impact of contaminated milk in Mexico.     

Determination of ochratoxin A in organic and non-organic cereals and cereal products from Spain and Portugal

The objective of this work was to know the occurrence of OTA in organic and non-organic cereals and cereal products from Spain and Portugal. A method based on extraction with matrix solid phase dispersion (MSPD) using octylsilica (C₈) followed by liquid chromatography coupled with fluorescence detection (LC–FD) was used to determine OTA from the selected samples. Recoveries of OTA from the studied samples spiked at 10 ng/g level ranged from 78% to 89% with a standard deviation of 3.66. The limits of detection and quantification of this method were 0.05 and 0.19 ng/g, respectively. Furthermore, LC–FD after OTA methylation was used to confirm the identity of OTA in all positive samples. This procedure was applied to 83 organic and non-organic samples including rice, wheat, barley, rye, oats and maize from Spain and Portugal. OTA was detected in 22% of the samples, with concentrations ranging from 0.20 to 27.10 ng/g. From the total OTA contaminated samples (n = 18), 72% were organic cereal and 28% were non-organic cereal samples, with mean concentrations of 1.64 and 0.05 ng/g, respectively. The 66% and 34% of contaminated samples were from Spain and Portugal, respectively, with mean concentrations of 0.93 and 0.64 ng/g for each country. Six contaminated samples exceeded the maximum limits (ML) for OTA fixed by European Commission Regulation (5 μg/kg), among them three were from Spain and three from Portugal.     

Growth kinetics of Listeria monocytogenes and spoilage microorganisms in fresh-cut cantaloupe

The main objective of this study was to investigate the growth kinetics of Listeria monocytogenes and background microorganisms in fresh-cut cantaloupe. Fresh-cut cantaloupe samples, inoculated with three main serotypes (1/2a, 1/2b, and 4b) of L. monocytogenes, were incubated at different temperatures, ranging from 4 to 43 °C, to develop kinetic growth models. During storage studies, the population of both background microorganisms and L. monocytogenes began to increase almost immediately, with little or no lag phase for most growth curves. All growth curves, except for two growth curves of L. monocytogenes 1/2a at 4 °C, developed to full curves (containing exponential and stationary phases), and can be described by a 3-parameter logistic model. There was no significant difference (P = 0.28) in the growth behaviors and the specific growth rates of three different serotypes of L. monocytogenes inoculated to fresh-cut cantaloupe. The effect of temperature on the growth of L. monocytogenes and spoilage microorganisms was evaluated using three secondary models. For L. monocytogenes, the minimum and maximum growth temperatures were estimated by both the Ratkowsky square-root and Cardinal parameter models, and the optimum temperature and the optimum specific growth rate by the Cardinal parameter model. An Arrhenius-type model provided more accurate estimation of the specific growth rate of L. monocytogenes at temperatures <4 °C. The kinetic models developed in this study can be used by regulatory agencies and food processors for conducting risk assessment of L. monocytogenes in fresh-cut cantaloupe, and for estimating the shelf-life of fresh-cut products.